CompilerInvocationException

[Paul Backus]

On Sunday, 26 February 2023 at 02:33:21 UTC, guacs wrote:
> NOTE: The error is happening when I'm using the SumType and I 
> suspect that I'm using it incorrectly.

I am not sure whether this is the specific error that is causing 
your problem, but there is  a mistake in your use of `SumType` in 
`expr.d`. [1]

On line 10, you declare

     alias Expression = SumType!(Number, Binary, Unary, Group);

Later, you declare `Binary` and `Unary` like this:

     struct Binary {
         Expression leftOperand;
         Expression rightOperand;
         Token operator;

         // etc.
     }

     struct Unary {
         Expression operand;
         Token operator;

         // etc.
     }

Since `Expression` contains `Binary` and `Unary`, and `Binary` 
and `Unary` contain `Expression`, that means `Expression` 
contains itself--which is not allowed, because it would result in 
`Expression.sizeof` being infinite.

The fix is to change `Binary` and `Unary` so that they contain 
*pointers* to `Expression`, like this:

     struct Binary {
         Expression* leftOperand;  // pointer
         Expression* rightOperand; // pointer
         Token operator;

         // etc.
     }

     struct Unary {
         Expression* operand; // pointer
         Token operator;

         // etc.
     }

[1] https://github.com/VisakhChekur/meval/blob/error/source/expr.d